Thermopile flame detector for combustion devices



Jan. 16, 1951 c. M. GARDINER ET AL 2,538,642

THERMOPILE FLAME DETECTOR FOR COMBUSTION DEVICES I Filed Aug. 51, 1949 FUEL SHUT OFF /a Inventors:

Cecil M.Garoliner-,

Arne LoFt',

Their At'brfley.

i atcnteti Jan. 16, 1951 NlTEl) STATES PATE OFFICE THERMOPILE FLAME DETECTOR FOR COMBUSTION DEVICES Cecil M. Gardiner and Arne Loft, Schenectady, N. Y., assignors, to General Electric Company, a corporation of New York I Application August 31, 1949, Scrial'No. 113,296

4 Claims.

'Many different arrangements have been considered for indicating the presence of flame in combustion apparatus, including certain thermopile devices.

fact that they did notwork equally well with various fuels. It is of course desirable that many different fuels may be used'ina gas turbine combustion chamber, for instance the heavy residual oils known as bunker C, those more highly refined oils used as Diesel engine fuel, ordinary kerosene, various gasolines, and gaseous fuels such as artificial or natural gases. These fuels have widely varying burning characteristics, and the flames they produce are considerably diiferent in their radiating power. Since a thermopile flame detector of the type described depends principally on the radiant heat received from the flame, it has been found difllcult to build such a detector which will work satisfactorily regardless of the type of fuel used.

' Accordingly an object of the present invention is to provide an improved flame detector of the thermopile type which will work well with all types of flame, regardless of the fuel particle size or radiating power of the flame.

Another object is to provide a thermopile flame detector having satisfactory rapidity of response,

' both when flame is initiated and when it is extinguished.

A furtherobject is to provide an improved tion with the accompanying drawings, in which Fig.4 is a diagrammatic representation of a portion of a gas turbine powerplant showing the arrangement of a. flame detector in accordance with theinvention; Fig. 2 is a sectional view of the'flame detectormounted in proper relation to the gas turbine combustor taken on the plane 2-.2 inFig. 1; Fig. 3 is an end view in elevation of the flame detector; Fig. 4 is an elevation view of the other end of the detector; and Fig. 5 is a Difilculty has been experienced with the previously knowndevices due to the flame detector having greatly lengthened life, yet

, 7 z shown mounted in proper position in the combustion system of a gas turbine powerplant, in

which a compressor of any suitable type, in-

dicated, generally at I, supplies air at a suitable pressure, for instance 75 lbs. per square inch, gage, through diffusing passages 2 and transition passages 3 to the combustor indicated generally at 4. The'combustor includes an outer housing '5 surrounding and spaced from an inner liner assembly 6, which latter defines the combustion space. The liner may be supported from the outer housing by any suitable means, for instance suitable radially extending brackets I. Substantially closing one end of the liner is an end dome 8 which is spaced from the inner surface of the liner 6 to form an annular nozzle for discharging a high velocity jet of cooling air along the inner surface of liner' wall 6, as indicated by the arrow 9.

For introducing liquid fuel in a finely atomized spray into the end dome ,8, a nozzle [0 is provided. This may be of any suitable type, but is preferably as shown in the copending application of B. 0. Buckland and D. C. Berkey, Serial No. 62,634, filed November 30, 1948, and assigned to the same assignee as the present application. As will be.apparent from Fig. 2 of the drawings, this nozzle is secured to a mounting boss 2| formed on the exterior surface of the outer casing 5, and is adapted to inject a conical spray of atomized fuel particles into the end dome 8, as indicated by the dotted lines II. For igniting the fuel-air mixture, an electric spark plug [2 is secured to the outer housing wall 5 and projects through the inner liner 6 and end dome 8 so that the electrodes provide a spark gap located approximately in the fuel spray pattern H. Fuel is supplied to the nozzle Ill through a supply Illa containing a solenoid operated shut-01f valve l3. If the nozsectional view of the end portion of the flame detector taken on the plane 5-5 in Fig. 2.

, Referringnow more particularly to Fig. 1, a flame detector incorporating the invention is zlelll is of the air-atomizing type disclosed in the above-mentioned Buckland and Berkey application, atomizing air at a suitable pressure is supplied through conduit lllb. Of course, with gaseous fuels a different style of nozzle, not provided with atomizing air, would be employed.

The exact details of the compressor, combustor, fuel nozzle, and other components are not essential to an understanding of the present invention; however, it may be noted that the combustor illustrated is of the general type disclosed in the application of Mr. A. J. Nerad, Serial No. 750,015, filed May 23, 1947. An important characteristic of this type of combustor is that the combustion supporting air is injected through circumferential rows of openings 6a at such bore Illa.

' pressure and velocity as to form strong discrete jets which persist all the way to the center of the liner, diametrically opposed jets meeting at the axis of the liner to produce a resultant velocity back towards the dome 8, this reverse circulation being represented by the axial air flow arrows l4.

The flame detector itself, to which the present invention particularly relates, is shown generally at l5. It will be apparent that the detector is secured to the outer housing 5 by any suitable means, for instance two or more mounting bolts IS. The major components of the flame detector are contained within a cylindrical barrel ll of a length to extend completely across the annular air supply space defined between combustor walls 5, 6, with the extreme end portion of the flame detector located in a circular opening formed in the inner liner of wall 6, as may be seen more clearly in Fig. 2. The outer end portion of the flame detector comprises a cylindrical member l8 adapted to receive a suitable electrical connector plug for coupling the flame detector to a suitable electric amplifier indicated generally at Ill. The specific type of amplifier employed is not material to the present invention.

The amplifier is of course supplied with power from a suitable source, and delivers an electrical output, in accordance with the signal received from the flame detector, to an electrical control device for modifying the operation of the powerplant. This may, for instance, take the form of a solenoid-operated valve l3, which is arranged to close and shut off the supply of fuel to the nozzle I whenever the flame in the combustor becomes extinguished. It will of course be obvious to those Skilled in the art that a signalling or indicating device or other arrangements for modifying in a desired manner the operation of the powerplant may be actuated by the flame detector.

The internal structure of the flame detector I is shown more particularly in Fig. 2. It will be seen that the mounting bolts l6 pass through a flange 20 suitably secured, as by welding, to the end of the barrel H, the bolts l6 being threadedly received in the mounting boss 2| with'a suitable gasket 22 between boss 2| and flange 20. The gasket is of course for the purpose of preventing leakage ofthe high pressure air outwardly around the flame detector. The electrical coupling member 18 is exteriorly threaded to receive an internally threaded member of the electrical connector. Member I8 is also provided with a radially extending flange 23 through which pass four machine screws 24 for securing flange 23 to flange 20.

Pressed, molded, or otherwise secured in the internal bore l8a of the electrical coupling member isan insulating body 25 in which are secured two electrical contact prongs 26. The insulating bushing 25 may be of any suitable type, but is preferably of a high temperature resistant molded plastic material, such as the polystyrene plastic known to the trade as Amphenol. Obviously other plastic or ceramic insulating materials, such as those well known in the spark-plug art may also be employed. It will be seen from Fig. 2 that the contact prongs 26 project at both ends from the insulating body 25, the upper end being a reduced diameter prong 26a adapted to engage a suitable electrical connector plug received in the Fig." 3 is an end view in elevation showing more clearly the shape of the mounting flanges 20, 23, and the arrangement of the rea 4 spective threaded fastenings I 6, 24 and the electrical contact prongs 26a. H

Located in the bore Ila, which extends entirely through the barrel I! of the flame detector, is a cylindrical insulating member 21 having a cylindrical recess 28 into which the electrical prongs 26 project and a pair of spaced axial holes 29 for accommodating the electrical leads for the thermo-pile, as described hereinafter.

For supporting the wires forming the thermopile, a third insulating cylinder member 30 is located near the inner end of the barrel l1. It will be seen in Fig. 2 that the extreme inner barrel end portion llb has a reduced diameter bore [10 forming a shoulder against which the insulator 30 is located. A locating dowel 30a is secured in the barrel l1 and projects into an axial groove in the outer surface of insulator 30 to prevent accidental rotational displacement thereof. It is to be particularly noted that the bore portion llc constitutes a protected recess in which the hot junctions of the thermopile are located, which is important for a reason noted hereinafter.

A cylindrical spacer member 3| holds the insulators 30, 21 in proper axially spaced relation. This metal spacer 3| is not a solid ring but is divided into two halves, along a longitudinal plane, which can be'readily assembled in a radial direction between the insulators 30, 21 so as to inclose the thermocouple wires described hereinafter. It will be obvious from Fig. 2 that the two halves of this spacer member 3| are contained within the bore Na and are engaged at either end by the insulating bodies.

A suitable resilient ring 32. made for instance of a temperature resisting artificial rubber such as the silicone rubbers is located between the beveled end surface of the coupling member I8 and the adjacent annular end surface of the insulator 21. It will now be apparent that tightening the four machine screws 24 will force the coupling member l8 inwardly so as to compress the ring 32 to seal the clearance space between the coupling member l8 and the barrel 11. This biasing force exerted by the couplingmember l8 will also force the insulating bodies" 30, 21 and the spacer halves 3| into their proper assembled location in the bore portion Ha. While they may be made of any suitable materials, inthe first engineering samples, the insulators 21 and 30 were machined from blocks of soap-stone. In large scale production these parts might be molded porcelain insulators as used in conventional spark-plug practice.

The thermopile proper is arranged as follows. As may be seen in Fig. 5, taken in connection with Figs. 2 and 4, the thermopile consists of a plurality of thermocouples connected in series relation. Each consists of a pair of thermo-electrically dissimilar metals, such as those which have become well known to the trade as ChromeP' Ni, 10% Cr) and Alumel Ni, 2% Al, 2% Mn, 1% Si). The Alumel wire segments are the ones indicated at 33 in'Figs. 4 and 5, while the Chromel portions are those indicated at 34. These respective wire portions 33, 34 are welded together at 35 to form the "hot junctions of the thermocouples. It will be observed that the junction 35 is not at the exact center 'of the bore llc but is displaced so that unequal lengths of the wires 33, 34 are exposed to the flame in the combustion space. The longer exposed segment 34 is made of Chromel, since that material resists oxidation better than the Alumel. These wire segments 33, 34 pass through spaced parallel rows 01.

. axial holes at, :1 in the insulator :0. At the side 2 and to form leads 34a, 33a which are suitably secured as by. welding at 33 to connectin wires 40 which pass through the openings 29 in insulator 21 and are in turn secured at 4! to the contactprongs 26. I

' It is important to note that the col d junctions 38 of the thermopile are maintained at the temperature of the combustion air, flowing through the annular supply passage between the inner liner 6 and the outer housing 5. To this end, the side portions of the barrel l1 and spacers 3| are provided with large circular openings seen at 42, 42a in Figs. 2 and 5, and by dotted lines in Fig. 4. Since the flow of combustion supporting air in the annular passage between walls 5, 6 is in a substantially axial directiomcooling air flows freely straight through the openings 42, 42a and across the cold junctions 38, as indicated by the aligned airflow arrows 43, 44 in Fig. 5. Thus the cold Junctions 38 are maintained very accurately at the temperature of the air supplied to the combustion space. 4

. In order to prevent overheating of the thermo-.

pile wires at the opposite side of the insulator 30,

a cooling air passage is provided through the insulator. This is in the form of an elongated slot 45 three views of which are. shown in Figs. 2, 4, and 5. As indicated by the air flow'arrow 46 in Fig. 5, a portion of the combustion air passes through the slot 45 and is discharged in a high velocity jet across the exposed hot portions .of the Chromel wires 34. It will be observed that this passage 45 is arranged at an oblique angle to the cooling air flow 43 and produces a jet which is not discharged directly at the hot junctions 35 but onto the Chromel wire portions 34. It has been found that this arrangement gives superior performance, as compared with earlier samples in which an axial hole through the insulator 30 produced a jet which discharged directly onto the hot junctions. With the present arrangement,

the hot junctions 35 and the. exposed portions of the wires 33 are cooled by the conduction of heat to the air-cooled portions 34. It will also be seen in Fig. 5 that a substantial length of the respective wires 33, 34 is exposed to the comparatively cool combustion supporting air at the cold side of insulator 30, so that any heat traveling by conduction along the wires from the hot side of the insulator 30 will be removed by this cooling air flow before it gets as far as the cold junctions 38.

The operation of the flame detector will be seen from the following. In starting the powerplant, the compressor vI is caused to rotate by an external starting motor (not shown) until the air supplied to the combustor is of a volume flow and pressure adequate to produce a good air-fuel mixture when liquid fuel is injected through the nozzle l0. Of course the automatic shut-off valve l3 must b provided with some means, for instance the manual operating lever |3a for opening the shut-off valve during thestarting cycle when there is no flame in the combustor. With valve [3a open, fuel being supplied through the supply line Ina, and air supplied from compressor l, the spark plug i2 is energized by a suitable ignition system (not shown), whereupon burningbegins.

As long as air under pressure is flowing from the, compressor through the supply passage between walls 5, 6 and through the flame detector 6 as indicated by'the arrows 43,- 44, 46 in Fig. 5, both the coldjunctions 33 and the hot junctions 35o! the thermopile will be maintained at the same temperature, namely that ofthe combustion supporting fluid. As long as this condition obtains, there is of course no net electrical output from the thermopile. On the other hand, when a flame is present within the liner 6, the hot junctions 35 are strongly heated by direct radiation from the flame. .The insulator serves ergy from reaching the cold junctions 38, which latter continue to be maintained at the tempera- I ll ture of the combustion supporting fluid. There is now a temperature difference between the cold and hot junctions, producing a net electrical output, which output is multiplied by the fact that the thermopile consists of eight thermocouples in series relation. The total net signal i very greatly increased by the amplifier IS, the resulting output of which is adequate to hold the fuel shut-oil. valve l3 in open position. When the flame is extinguished, the air flowing over the cold junctions and the exposed portions of wires 34 quickly brings both hot and cold junctions to the same temperature, whereupon the electrical signal fails and the valve I3 is caused to close.

It may now be noted that one reason why the cooling air slot is inclined as shown in Fig. 5 is to prevent radiant energy passing directly through this passage and impinging on the cold junctions 33. With the angle of the slot as shown in Fig. 5, coupled with the fact that the cold junctions 3B are offset to the right from the cen terline of the flame detector, direct radiation from the flame to thecold junctions is prevented. In other words, the oblique slot arrangement facilitates passage of cooling air in one direction but prevents the passage of radiant heat energy in the opposite direction.

It is to be noted that this flame detector is not responsive to the absolute temperature of the combustion gases but to the difference in temperature between the hot reaction products inside the liner 6 as compared with the cooler combustion supporting air flowing between the walls 5 and 6. This is of considerable importance in a gas turbine powerplant since the range of operation from minimum fuel and airflow to maximum, with the wide variation in ambient temperatures encountered, is such that in certain portions of the operating range the temperature of the combustion air (when there is no flame inside the liner) may actually be higher (by reason of the heat of compression added in the compressor I) as compared with the temperature of the hot burning gases within the liner in certain other portions of the range of operation. For this reason, merely measuring the absolute temperature of the fluids inside the liner 6will not give a reliable indication as to whether or not there is flame present. But the temperature difference between the air supplied to the combustor and the fluid within the linen-will be a satisfactory indication of the presence of flame, since a temperature rise from the air supply passage to the combustion space will occur only when heat release takes place. Thus this thermopile is basically an electrical instrument for detecting a temperature rise in a fluid flowing through the combustion system, which necessarily accompanies any heat releasing reaction occurring within the liner.

Experience with flame detectors made in ac cordance with the invention has shown that they are quick and reliable in operation, being capable of detecting the initiation of flame within the combustor with a time delay of perhaps only 1 or 2 seconds. When combustion ceases within the liner, the time interval required for "dropout is somewhat longer, perhaps on the order of 3 to seconds. This is due to the fact that it takes a short time for all the burning gases to be blown out of the combustion space by the air which continues to be supplied by reason of the rotational inertia of the compressor I. A perhaps more important factor is that the liner wall 6, and other interior portions of the combustor may be operating at or near red heat, so that these hot parts continue briefly to radiate heat to the thermopile even though the flame has disappeared. When combustion ceases, these parts are of course rapidly cooled by the air flowing through the combustor but they remain hot long enough to introduce a slight delay in the response of the thermopile.

In this connection, it may be noted that a very substantial improvement in the response of the thermopile is effected by having the hot junctions recessed back into the bore portion llc so as to be shielded from direct contact with the fluids within the combustion space. more, the skirt portion llb of the barrel I1 is cooled by the air flowing around it; therefore this skirt also serves as a radiation shield protecting the hot junctions from energy emitted by hot portions of the combustor after the flame has ceased. This shielding arrangement for the hot junctions 35 is also important in that it prevents raw fuel particles projected by the nozzle from collecting on the wires forming the thermopile. In previous models it had been found that, with the hot junctions more exposed, fuel tended to collect on the wires and then burn there, with consequent overheating of the thermocouple wires and serious shortening of the life of the device. Whereas the previous devices burned out after only about one to ten hours of operation, a sample device made in accordance with the invention appears to have almost indefinite life. Specifically, one unit ran for three hundred hours without any sign of failure or deterioration. At the same time, this improved detector is so simple in mechanical arrangement that it costs only about half as much as previously known devices;

An extremely important advantage of this-1m proved flame detector lies in the fact that it has been found capable of operating equally well with a wide variety of fuels, ranging from extremely heavy liquids such as bunker C oil to gaseous fuels such as natural gas, in spite of the widely varying characteristics of the flames produced by these fuels. Thus with the invention it is not necessary to change the flame detectors used when the type of fuel is changed.

While only one specific embodiment of the invention has been described in detail, it will be apparent to those skilled in the art that many modifications in the mechanical arrangement of the detector may be made, and we desire to cover by the appended claims all such changes as fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In a flame detector for a combustion device, the combination of a cylindrical barrel having a central axial bore, a cylindrical insulating body disposed in said bore and spaced axially from the forward end thereof, said insulating body having first and second transversely spaced rows of axial holes for receiving thermopile wires and Furthera cooling air slot between said rows of holes, said slot being at an acute angle to the axis of the insulator and having a first end portion opening adjacent the first row of holes at the hot side of the insulator and a second end portion opening adjacent the second row of holes at the cold side of the insulator, the forward extending end portion of the barrel forming a shield restricting the direct impingement on the exposed wires of fluids inside the combustion space and of radiant heat from the hot walls thereof, and an electrical thermopile supported by the insulator and comprising a first set of parallel wires of a metal having comparatively good temperature and corrosion resistance and disposed through said first row of holes, the end portions of the wires at the hot side of the insulator extending transversely across the open end of the cooling air slot and terminating between said slot and the second row of holes, the other ends of said wires at the cold side of the insulator extending a substantial distance axially from the insulator whereby any heat traveling by conduction along the wires from the hot ends thereof is dissipated, the extreme end portions of the wires at the cold side of the insulator extending transversely and terminating between the first row of holes and the cooling slot opening at the cold side of the insulator, a second set of wires of electrothermally dissimilar metal disposed through the second row of holes with transversely extending end portions terminating adjacent the respective ends of said first set of wires, adjacent ends of the respective pairs of dissimilar wires being fused together to form a plurality of thermocouples in electrical series relation, said barrel defining openings for admitting combustion supporting fluid to said central bore at the cold side of the insulator, whereby the cold junctions of the thermocouples are maintained substantially at the temperature of the combustion supporting fluid and a portion of the fluid flowing through said openings is caused to be diverted through said cooling fluid slot and discharged across the hot exposed portions of said first set of wires without directly impinging on the hot junctions of the thermocouples.

2. In a fiame detector for a combustion device having walls defining a combustion space and an air supply passage, the combination of a cylindrical barrel having a bore extending entirely therethrough with an annular locating shoulder adjacent but spaced axially from the forward end of the barrel, a first cylindrical insulating body disposed in said bore against the locating shoul der and having first and second transversely spaced rows of axial holes for receiving thermopile wires and a cooling air slot between said rows of holes, said slot being at an acute angle to the axis of the insulator and having a first end portion opening adjacent the first row of holes at the hot side of the insulator and a second end portion opening adjacent the second row of holes at the cold side of the insulator, the extreme end portion of the barrel forming a shield restricting the direct impingement on the exposed wires of fluids inside the combustion space and radiant heat from the hot walls thereof, a second cylindrical'insulating body disposed in an intermediate portion of the barrel and axially spaced from the first insulator and having two axial passages communicating with a cylindrical recess at the side of the second insulator remote from the first insulator, a spacer sleeve member located between and having end porbustion supporting fluid is supplied freely to the,

bore of the barrel at the cold side of the first insulator, a first radially extending mounting flange secured to the cold end portion of the barrel and adapted to be secured to the outer wall of the combustion device with the intermediate portion of the barrel extending through the air supply passage and the extreme hot end of the barrel projecting through an opening in the combustion space wall, an electrical coupling member comprising a hollow cylindrical member with an externally threaded end portion for receiving a coupling sleeve, the other end of the coupling member containing a third insulating cylinder member having two contact prong members each with one end portion extending into said threaded end portion of the coupling member and adapted to b engaged by an electrical connector plug, the other end portion of each prong extending into said recess in the adjacent end of the second insulator, the inte.;- mediate portion of the coupling member forming a radially extending flange adapted to be secured to said first mounting flange, the adjacent circumferential portions of the second insulator, coupling cylinder member, and barrel bore defining an annular recess, a resilient sealing ring disposed in said annular recess, fastening means for drawing said second flange on the coupling cylinder member tightly against said first mounting flange whereby the first and second insulators and the spacer sleeve are secured in the barrel and the resilient ring is compressed into sealing engagement with the second insulator coupling member and barrel to prevent fluid leakage therebetween, and a thermopile supported by the first insulator and comprising a first set of parallel wires of a metal having comparatively good temperature and corrosion resistance and disposed through the first row of holes in the first insulator, the end portions of the wires at the hot side of the insulator extending transversely across the open end of the cooling air slot and terminating between the cooling slot opening and the second row of holes, the other ends of said wires at the cold side of the insulator extending a substantial distance axially from the insulator whereby any heat travelling by conduction along the wires from the hot ends thereof is dissipated, the extreme end portions of the wires at the cold side of the insulator extending transversely and terminating between the first row of holes and the cooling slot opening at the cold side of the insulator, a second set of wires of electro-thermally dissimilar metal disposed through the second row of holes with transversely extending end portions terminating adjacent the respective ends of said first set of wires, adjacent ends of the respective pairs of dissimilar wires being fused ogether to form a plurality of thermocouples i series relation, and a pair of lead wire members disposed through the axial holes in the second insulator and having end portions fused to the respective f nds of the dissimilar wire sets and 10 to the ends of said contact prongs in the recess in the second insulator.

3. In a flame detector for a combustion device, the combination of a hollow cylindrical barrel member, a cylindrical insulating body disposed in the barrel and spacedaxially from the forward end thereof, said insulating body having a cooling air slot extending axially therethrough at an acute angle to the axis of the insulator, the forward extending end portionof thee-barrel forming a shield" adapted to restrict the direct impingement on the exposed wires of fluids in the combustion space and of radiant heat from the hot walls of the chamber, and an electrical thermopile comprising a first set of parallel wires of a metal having comparatively good temperature and corrosion resistance disposed through the insulating body in a transverse row adjacent one end opening of the cooling air slot, the end portions of said wires at the hot side of the insulator extending transversely across the adjacent open end of the cooling slot, the other ends of the wires at the cold side of the insulator extending a substantial distance axially from the insulator whereby any heat traveling by conduction along the wires from the hot ends thereof is dissipated, a second set of wires of electro-thermally dissimilar metal disposed through the insulator in a transverse row parallel to and spaced from said first row of wires and having transversely extending end portions terminating adjacent the respective ends of the first set of wires, adjacent ends of the respective pairs of dissimilar wires being fused together to form a plurality of thermocouples in electrical series relation, said barrel having two diametrically opposed openings for passing a comparatively cool combustion supporting fluid transversely through the barrel and over the cold junctions of the thermocouples whereby the latter are maintained substantially at the temperature of the combustion-supporting fluid while a portion of the fluid flowing through said openings is caused to be diverted through the cooling fluid slot and discharged across the hot exposed portions of said first set of wires without directly impinging on the hot junctions of the thermocouples.

4. A flame detector for a combustion device comprising a hollow cylindrical barrel, a cylindrical insulating body disposed in the barrel and spaced axially from the forward end thereof, said insulating body having a cooling fluid slot extending axially therethrough, the forward extending end portion of the barrel forming a shield restricting th direct access of the fluids inside the combustion space and the impingement of radiant heat from the hot walls of the chamber, and an electrical thermopile comprising a first set of wires of a metal having comparatively good temperature and corrosion resistance disposed through the insulating body adjacent one end opening of the cooling slot, the end portions of said wires at the hot side of the insulator being disposed within the sheltered recess defined by said shield and extending transversely across the adjacent open end of the cooling slot, the other ends of the wires at the cold side of the insulator extending a substantial distance axially from the insulator whereby any heat traveling by conduction along the wires from the hot ends thereof is dissipated, a second set of wires of electro-thermally dissimilar metal disposed through the insulator and having transversely extending end portions terminating adjacent the respeetive-"ends ofthe first-set of wires, adjacent ends of the respective pairsoi' wires bein'gfused together to form a pluraiity of thermocouples in electrical series relation, said barrel having diametrically opposed openings idr passing comparatively c001 combustionsufipo'rting fluid transversel through the barrel and ever the cdld' junctions of the thermocouples whereby the latter are maintained substantially at the temperature -0f'thecombustionsuppbrt ing fiuid while aportion or said fluid is diverted Number j ame v through" the eodli'ng slot and discharged across 3 "Alfery June 22, 1943 the'hot exposed porti'ons of said first set ofwire's, 2,340,899 Ray L... Feb. 8,194 4 the hot junc tion s' r the thermrzdupl'esubeinz 3 Ray ay 1. 194 f charged by said eooling slot wherein? the 900i- Jun-cam I I a f y CECIL M1=GARDINER f CITED fileqf this Patent: J In UNITEDSTATES PATENTS. 

